This invention relates generally to the treatment of crude oil streams to prevent fouling by inorganic materials. In one aspect, the invention relates to the prevention or reduction of inorganic fouling in crude oil heat exchangers using the salts of polyacrylic acid and its derivatives.
The fouling of refinery equipment by crude oil has long been recognized. Such fouling not only damages equipment and reduces the effectiveness of heat exchange equipment, but also adds expense to the operation in that frequent shutdown times may be required to remove the fouling deposits.
The fouling by crude oil at the heat exchanger upstream of the refinery distillation unit is particularly critical since the heat exchange tubes are generally small and cannot tolerate the buildup of solids.
Fouling may be due to a variety of causes, including fouling by asphaltenes, fouling by polymerization of olefins, and fouling by oxidation, and fouling by deposition of inorganic impurities in the crude. Antifoulants for crude oil are formulated to combat the type of fouling encountered. For example, a variety of polyamines are available for inhibiting asphaltene fouling (see U.S. Pat. No. 4,619,756, column 4). Nitroxide compounds and antipolymerization additives are available for treating monomers to prevent polymer fouling (see U.S. Pat. No. 4,670,131). Antioxidants such as phenylene diamine and phenolic antioxidants are available for combating oxidation fouling.
Very few antifoulants for use in crude oil streams have been developed specifically for combating fouling by inorganic materials. These materials are present as impurities in the water phase of crude oil and include salts, silica, alumina, and corrosion by-products,s etc. Upon passing through the heat exchangers of the refinery these materials deposit on the heat transfer surfaces, reducing the heat transfer efficiency and/or plugging the equipment. All crudes have some water present. Even after desalting, there may be a trace to 0.5 percent of water which contains the inorganic impurities.
Fouling by the inorganic impurities in crude oil has long been recognized, as evidenced by U.S. Pat. Nos. 3,546,097 and 3,776,835. U.S. Pat. No. 3,558,470 describes the problems of inorganic impurities as causing complexes with organic deposits and oxidize derivatives resulting in the deposition of these materials as oil insoluble polymers and complexes. This patent suggests the use of an ashless dispersant and a phosphite type of antioxidant-antipolymerant compound. U.S. Pat. No. 3,776,835 identifies inorganic salts as foulants in crude oil and suggests the use of certain amines and amides in a hydrogen environment.
Both of these solutions appear to address the problem of asphaltene and/or unsaturated olefin fouling and oxidation fouling, with the role of inorganic materials as being part of the complexes, polymers, and oxidation products.